Just a few random thoughts, from a non-specialist but someone who does live in the Northwest and pays attention to the railroads and the history books.
I think neroden overstates the case for the Milwaukee a bit.
The GN is not awful. In Eastern MT it is flat and straight, Marias Pass is the lowest crossing of the divide available. It has only minimal waste of elevation (climbing only a few hundred feet to cross from the Flathead River drainage to the Koonetai River, once Haskell Pass was bypassed in 1903.)
For online traffic, it has its fair share of farm traffic. It did miss out on mining traffic at first but quickly rectified that with the line down to Butte (and moved a LOT of ore between Butte/Boulder/Wickes and a smelter in Great Falls that nobody remembers even existed.)
NP and MILW, by contrast, are roller coasters: up the Yellowstone, down the Gallatin, up the Jefferson, down the Clark Fork, and up the Musselshell, down 16 mile creek, up the Missouri/Jefferson, down the Clark Fork, up and over St. Paul Pass, respectively.
It boggles my mind that NObody took the most obvious route across Montana -- up the Missouri, cross Rogers Pass west of Great Falls, down the Blackfoot and Clark Fork. GN at least considered it (and rejected it because Marias was an easier pass.)
neroden cites the Milwaukee route as "best from Puget Sound to Spokane." Snoqualmie Pass has good grades, yes. The crossing of the Cascades should have been kept. Perhaps the bypass south of Spokane, and the St. Paul Pass route, should have been kept as the lowest-mileage route, vs. going up through Sandpoint (NP) and Bonner Ferry (ID), accepting the steeper grade for light time-sensitive traffic.
The unnecessary 2% grades in central Washington, crossing a range of hills that were in neither NP's nor GN's way, were just silly. The steepest grades on the entire Pacific Coast Extension are in the place that
looks like it has no mountains at all if you glance casually at the map.
Similarly in Montana one could compare grades and choose intelligently between Homestake and Pipestone, and between Bozeman Pass and 16 Mile Canyon. A half-NP-half-MILW route would be better than either NP or MILW was separately. A smarter (or wealthier in 1980) BN might have taken advantage of that.
The GN route might have been maintained east of Spokane as a sort of express freight bypass, or it might have been abandoned entirely.
BN made one big mistake here, abandoning the GN Spokane-Priest River-Sandpoint. They are now double-tracking the NP line, including the causeway across Lake Pend Orielle, at great expense, to regain the lost capacity. Both west of Spokane and east of Sandpoint they have a choice of routes.
(You might argue that not keeping both SP&S and NP between Pasco and Spokane was a similar mistake, but a less serious one.)
I think Mark goes a bit too far the opposite direction:
Blaming Milwaukee Road mismanagement is the ultimate copout. If a railroad has value, someone (even if not associated with that railroad) will see it and save it.
The Milwaukee was worth saving, at least in part, in the 60s. And
at that time there were interested parties. They then proceeded to run it into the ground for 10 years until the entire Pacific Coast Extension was one giant slow order desperately in need of new ties and ballast.
Closing the gap between the two electrified sections would have made the railroad a lot more appealing. Requiring 3 engine changes rather than 1 requires a lot of extra equipment and manpower. Manpower was a lot cheaper in 1915 than in 1973 or today.
But unless the extension sees a lot of maintenance investment in the late 60s... by 1972 I can see why a lot of folks thought it was a lost cause.
Maybe there was a window of opportunity right after the BN merger, if every dollar earned in new Puget Sound traffic was plowed into the deferred maintenance backlog.
Thing is, there wasn't any railroad anywhere in the country making huge investments in the future in the 1970s. Even "healthy" roads were lifting every rail they could and cutting every corner they could. It is unbelievable how much track, not just Milwaukee's, was abandoned in the 70s and early 80s. (I grew up in southern Idaho, and a look at UP branch lines is a litany of "not repaired after 1976 flood," "abandoned 1980", "abandoned 1981", "abandoned 1983" - to West Yellowstone, to Victor, to Sun Valley, to Fairfield, to Mackay, to Wells, NV (OK, I admit that line never made a heck of a lot of economic sense, once "sheep from Sun Valley to California" ceased to be a thing.) Something close to half of UP's route-miles in Idaho vanished in the space of ten years, leaving only the main line and the two heaviest-traffic branches.
With 20-20 hindsight, we would have saved a lot of medium traffic branch lines, and a couple key routes across Ohio that the National and Broadway Limited could be using, and the track between Richmond and Raleigh that VA and NC are talking about re-laying now, and...and...and... you could go on all day about that. In that context, running the Milwaukee into the ground was just a symptom of running the entire national system into the ground, and we are paying for that nationwide today.
